In film-screen radiography, an X-ray tube generates a beam of X-rays, which is aimed at a subject. The X-rays that pass through the patient are filtered through a device called an X-ray filter, to reduce scatter and noise, and strike an undeveloped film, which is held tightly to a screen of light-emitting phosphors in a light-tight cassette. The film is then developed chemically and an image appears on the film. In digital radiography, the X-rays strike a plate of sensors, referred to as a detector, that converts the signals generated into digital information, which is transmitted and converted into an image displayed on a computer screen. Accordingly, in a digital radiography system, a projection of the tissue density along the ray path is acquired as a two-dimensional image.
X-ray computed tomography (CT) is a technology that uses computer-processed x-rays to produce tomographic images as virtual slices of specific areas of the scanned object. Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional radiographic images taken around a single axis of rotation. The CT scanning is a measurement of the amount of X-rays absorbed in the specific volume elements constituting the three-dimensional image, and each volume element represents the density of the tissue comprised in the volume element. Medical imaging is the most common application of X-ray CT, and the cross-sectional images generated via CT can be used for diagnostic and therapeutic purposes in various medical disciplines.
Digital tomosynthesis combines digital image capture and processing with simple tube/detector motion as used in computed tomography (CT), however over a smaller rotational angle than that used in CT. One application of digital tomosynthesis is breast tomosynthesis, a three-dimensional imaging technology that involves acquiring images of a stationary compressed breast at multiple angles during a short scan. The individual images are then reconstructed into a series of thin high-resolution slices that can be displayed individually or in a dynamic mode. Reconstructed tomosynthesis slices reduce or eliminate the problems caused by tissue overlap and structure noise in single slice two-dimensional mammography imaging.